This invention relates to temperature control of a combustor in a fuel cell power plant which uses reformate gas.
Tokkai 2000-178001 and Tokkai 2000-185903 published by the Japanese Patent Office in 2000 disclose a temperature control of a vaporizer of a fuel cell power plant which uses reformate gas.
The fuel cell power plant is provided with a fuel cell stack which generates electricity by a reaction of reformate gas, a reformer which reforms vaporized fuel and generates reformate gas, a vaporizer which vaporizes liquid fuel, and a combustor which heats the vaporizer. The combustor burns anode effluent discharged from the anode of the fuel cell stack, and heats the vaporizer by combustion gas.
Supplementary fuel is also supplied to the combustor and the combustor burns the supplementary fuel together with the anode effluent to generate combustion gas. When liquid fuel supply to the vaporizer is increased, heat required to vaporize the liquid fuel is also increased. Accordingly the supply of supplementary fuel to the combustor is increased to increase the temperature of combustion gas. Methanol is used for the liquid fuel and supplementary fuel.
Supplementary fuel supplied to the combustor first vaporizes by the heat of the combustor, and thereafter is burnt to generate combustion gas. When the supply amount of the supplementary fuel is increased, the latent heat of vaporization is also increased that makes the temperature in the combustor temporarily fall. Although the combustion of the vaporized fuel thereafter raises the temperature, if the temperature by this temporary fall becomes lower than the combustion stall temperature, the combustion of the fuel in the combustor cannot be maintained.
According to the prior art, when the temperature in the combustor falls, the supplementary fuel supply is increased. As a result, the temperature of the combustor falls still further.
When the temperature of the combustor falls, the temperature of the vaporizer also falls. If there is a shortfall in the power generation amount by the fuel cell stack due to the temperature fall in the vaporizer, a secondary battery discharges power in order to fill up the shortfall in power generation. As a consequence, the load on the secondary battery is increased. When the temperature of the vaporizer falls, a part of the liquid fuel may be provided to the reformer without being vaporized. If the fuel in the liquid state flows into the reformer, it deteriorates the reforming performance of the reformer and increases the generation of carbon monoxide in the reformer. Carbon monoxide is known to cause the poisoning of the fuel cell stack and adversely affects the power generation performance of the fuel cell stack.
It is therefore an object of this invention to maintain the temperature of the combustor used for a fuel cell power plant within a preferred range.
In order to achieve the above object, this invention provides a fuel cell power plant, comprising a combustor which generates heat due to combustion of fuel, a vaporizer which applies heat provided from the combustor to a liquid source material and generate a vaporized source material, a fuel cell stack which generates electric power using the vaporized source material, a fuel supply device which supply fuel to the combustor, a sensor which detects a power generation requirement of the fuel cell stack, and a programmable controller.
The programmable controller is programmed to calculate a liquid source material supply amount to the vaporizer based on the power generation requirement, calculate a fuel supply amount of the fuel supply device based on the liquid source material supply amount to the vaporizer, calculate a prediction temperature of the combustor based on the fuel supply amount of the fuel supply device, and control the fuel supply amount of the fuel supply device to prevent the prediction temperature from falling below a predetermined temperature.
This invention also provides a control method for such a fuel cell power plant that comprises a combustor which generates heat due to combustion of fuel, a vaporizer which applies heat provided from the combustor to a liquid source material and generate a vaporized source material, a fuel cell stack which generates electric power using the vaporized source material, and a fuel supply device which supply fuel to the combustor. The control method comprises detecting a power generation requirement of the fuel cell stack, calculating a liquid source material supply amount to the vaporizer based on the power generation requirement, calculating the fuel supply amount of the fuel supply device based on the liquid source material supply amount to the vaporizer, calculating a prediction temperature of the combustor based on the fuel supply amount of the fuel supply device, and controlling the fuel supply amount of the fuel supply device to prevent the prediction temperature from falling below a predetermined temperature.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.